If you want to know more about your followers on Twitter and how influential they might be consider using Fruji, a webapp that gives extensive analytics on your followers.

Basic analytics are free but if you spring for the premium or pro packages you'll get additional information such as identifying new followers, spam followers, and find out what users have unfollowed you. They also track your mentions and follower demographics such as timezones and languages spoken.

You'll need to give Fruji read permission of your Twitter account and your email address, but the webapp doesn't try to access any additional privileges. As you can tell from the screenshot I'm not a heavy Twitter user so I'd have no interest in any of the premium packages, but if tracking social media penetration is important to your business it might be another weapon in your arsenal.